Not applicable.
The present invention relates to a method for making vegetable oil-based polyols. Still further, the present invention includes using vegetable oil-based polyols to produce polyurethane resins for use as casting compounds for electrical applications.
Polyols may be produced from petroleum. However, vegetable oils come from renewable resources. Vegetable oil molecules must be chemically transformed in order to introduce hydroxyl groups. For instance, soybean oil does not contain any hydroxyl groups but has on an average about 4.6 double bonds per molecule. The unsaturated portions of the vegetable oil molecule can be converted to hydroxyl groups. However, many reactions for preparing polyols from vegetable oils are not very selective. By-products, in addition to alcohol groups, are created during the transformation. Furthermore, many conventional methods of preparing polyols from vegetable oil do not produce polyols having a significant content of hydroxyl groups. Still further, many available methods of preparing polyols from vegetable oils do not produce products having a desirable viscosity. Greases or waxes often result as a consequence of such chemical transformations.
Conventionally, cast electrical components such as dry voltage transformers and insulators are formed from epoxy resins. Epoxy resins are rather expensive to use. Still further, epoxy resins are not easy to handle at low temperatures and have poor elasticity. Polyurethane resins prepared with castor oil have also been produced. However, these resins tend to be rubbery and thus undesirable for certain casting applications. Still further, castor oil-based polyurethanes have some limitations due to their higher price and environmental problems related to their by-products.
In order to overcome the deficiencies found with conventional processes for making vegetable oil-based polyols, a method for making vegetable oil-based polyols from vegetable oil or epoxidized vegetable oil is needed for a variety of applications including preparation of, through polyurethane chemistry, a resin for use as an electroinsulating casting compound, which is another embodiment of the present invention. Still further, this method of making vegetable oil-based polyols should avoid substantial side-reactions, such as esterification, cyclization, polymerization, and other undesirable reactions, and should produce polyols having a high hydroxyl content and a desirable viscosity.
It is an object of the present invention to provide a method for making polyols from renewable resources.
It is another object of the present invention to provide a method for making vegetable oil-based polyols directly from vegetable oil in a continuous two-step process so that unnecessary intermediate steps are avoided.
Another object of the present invention is to provide polyurethane resins made from vegetable oil-based polyols and methods for making the same in order to create polyurethane casting compounds having improved hydrolytic properties and improved thermal stability.
Still another object of the present invention is to provide a method for making vegetable oil-based polyols having a desirable viscosity and a high content of hydroxyl groups.
A further object of the present invention is to provide a casting resin made from vegetable oil-based polyols having improved mechanical and dielectric properties over conventional casting resins and a method for making the same so that a casting compound having excellent insulating properties and durability may be provided.
Still another object of the present invention is to provide a method for making vegetable oil-based polyols having a favorable distribution of hydroxyl groups in the molecule so that when these polyols are reacted with isocyanates to form polyurethanes, crosslinking within the polyurethane is optimized.
Still another object of the present invention is to provide a method for making various vegetable oil-based polyols having a range of hydroxyl content so that cast polyurethane materials having a range of glass transition characteristics may be created. Depending upon the type of vegetable oils used as the starting material, polyurethane resins ranging from soft nibber to rigid plastics may be created.
According to the present invention, the foregoing and other objects are achieved by a method for making vegetable oil-based polyols directly from vegetable oil using a consecutive two-step process involving epoxidation and hydroxylation. Specifically, this process comprises adding a peroxyacid to vegetable oil wherein said vegetable oil and said peroxyacid react to form epoxidized vegetable oil and adding said epoxidized vegetable oil to a mixture of an alcohol, water, and a fluoboric acid catalyst wherein the epoxidized vegetable oil undergoes hydroxylation so as to form a vegetable oil-based polyol.
The vegetable oil-based polyols created by this method may be reacted with isocyanates so as to form polyurethanes, which is another embodiment of the present invention. Alternatively, fillers such as silica may be combined with these vegetable oil-based polyols before they are reacted with isocyanates to form polyurethanes. In still another embodiment of the present invention, polyurethanes made from vegetable oil-based polyols may be used to form electroinsulating casting resins for use in electrical applications.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
The method of the present invention involves making vegetable oil-based polyols by converting each of the double bonds of the vegetable oil molecule into a hydroxyl group. This method takes place at approximately atmospheric pressure.
The process of the present invention involves epoxidation and subsequent hydroxylation of vegetable oil so as to make a polyol. More specifically, the process of the present invention includes adding a peroxyacid in a solvent to vegetable oil wherein said vegetable oil and said peroxyacid react to form epoxidized vegetable oil, and adding said epoxidized vegetable oil, which is in the solvent, to a mixture of an alcohol, water, and a catalytic amount of fluoboric acid so as to form a vegetable oil-based polyol. These are consecutive, non-stop steps. The reaction is not stopped after the epoxidized vegetable oil forms so as to purify the intermediate product.
Any vegetable oil may be used in this process. Examples of vegetable oils that may be used include, but are not limited to, soybean oil, safflower oil, linseed oil, corn oil, sunflower oil, olive oil, canola oil, sesame oil, cottonseed oil, palm oil, rapeseed oil, tung oil, fish oil, or a blend of any of these oils. Alternatively, any partially hydrogenated vegetable oils or genetically modified vegetable oils can be used to obtain the desired hydroxyl content. Examples of partially hydrogenated vegetable oils or genetically modified vegetable oils include, but are not limited to, high oleic safflower oil, high oleic soybean oil, high oleic peanut oil, high oleic sunflower oil and high erucic rapeseed oil (crambe oil). The iodine values of these vegetable oils range from about 40 to 240 and more preferably from about 80 to 240. When vegetable oils having lower iodine values are used to make vegetable oil-based polyols, polyols with lower hydroxyl numbers and thus lower viscosities are created.
Any peroxyacid may be used in the epoxidation reaction. Examples of peroxyacids that may be used include, but are not limited to, peroxyformic acid, peroxyacetic acid, trifluoroperoxyacetic acid, benzyloxyperoxyformic acid, 3,5-dinitroperoxybenzoic acid, m-chloroperoxybenzoic acid, or any combination of these peroxyacids. The peroxyacids may be formed in-situ by reacting a hydroperoxide with the corresponding acid, such as formic or acetic acid. Examples of hydroperoxides that may be used include, but are not limited to, hydrogen peroxide, tert-butylhydroperoxide, triphenylsilylhydroperoxide, cumylhydroperoxide, or any combination of these hydroperoxides. Preferably, the peroxyacid is in a solvent such as acetic acid, formic acid, or chloroform.
Fluoboric acid is used as the acid catalyst in the hydroxylation step. Using fluoboric acid as a catalyst in this hydroxylation reaction works better than using other inorganic acids suggested by the prior art. Specifically, by using fluoboric acid, the vegetable oil-based polyol produced consistently has a higher hydroxyl content. A catalytic amount of fluoboric acid is used in this reaction, which should be about 2% or less by weight of the amount of epoxidized vegetable oil used.
Examples of alcohols or alcohol mixtures that may be used in the hydroxylation reaction include, but are not limited to, monoalcohols such as methanol, ethanol, propanol, and butanol. It is desirable to have methanol be part of the alcohol mixture used in the hydroxylation reaction because it is the most reactive alcohol. However, if methanol is used alone, undesired cleavages of the triglyceride occur. Preferably, the alcohol used in the hydroxylation reaction is a mixture of methanol and isopropanol. Other alcohol mixtures may also be used so long as the methanol concentration is kept low. In fact, methanol may be used with solvents other than alcohols, such as chloroform, toluene, formic acid, or acetic acid. It is important during the hydroxylation step to always have an excess amount of alcohol present so as to prevent polymerization and the formation of products having higher viscosities.
Water is also an important component in this reaction. It reacts with the epoxy groups of the epoxidized vegetable oils to form two hydroxyl groups per epoxy group in some location so as to increase the hydroxyl content of the vegetable oil-based polyols. Specifically, water contributes to about 10% or lower dihydroxylation of the vegetable oil. Still further, it acts as a diluent to the fluoboric acid so that the acid is not reactive towards undesired cleavage of the triglyceride linkages present in the vegetable oil molecules.
The molar ratio of water to epoxy groups is from about 1:1 to about 10:1. In a preferred embodiment of the present invention, where a mixture of methanol and isopropanol is used as the alcohol in the hydroxylation reaction, the molar ratio of methanol to epoxy groups is from about 1:1 to about 10:1 and preferably is about 4:1 to about 10:1. The molar ratio of isopropanol to epoxy groups is from about 5:1 to about 10:1 and preferably is about 8:1.
The epoxidation reaction occurs at approximately room temperature or between about 20 and 30xc2x0 C. During the hydroxylation step, the temperature rises. The extent to which the temperature rises depends upon the amount of solvent present. If the temperature rises to less than 50xc2x0 C., it is preferable to increase the reaction speed by warming the reaction mixture to this temperature.
The vegetable oil-based polyols made by the method of the present invention have a viscosity in the range of 1,000-7,000 centipoise at room temperature. The viscosity of these polyols is lower than vegetable oil-based polyols made by other methods because the method of the present invention avoids substantial side-reactions, such as polymerization or crosslinking. Still further, the vegetable oil-based polyols made by the method of the present invention have a hydroxyl content ranging from 110 to 213 mg KOH/g. Preferably, the polyol has a high hydroxyl content which equals to approximately one hydroxyl group per double bond of the vegetable oil. Vegetable oil-based polyols can be made in yields of 85-95% using any of the various embodiments of the process of the present invention.